Skip to main content

Full text of "Text Book Of Mechanical Engineering"

See other formats





$22                             Appendix IL

^The 'rack' is represented by the gang of cutters A, which simul-
taneously rotate and travel slowly in an axial direction. While
cutting takes place, however, the blank is also rotated on its own
axis, by means of change wheels, in such wise as to accurately
roll upon the (rack,5 with no slip whatever. The consequence is,
that the spaces cut out are not quite of the same shape as the
•cutter teeth, but are so widened that a real rack of the cutter
section would roll perfectly with the wheel thus cut. The axial
traverse of the cutters is given by the fixed cam c, which gradually


thickens from D to E, through about three-quarters of a turn, and
returns rapidly between E and D. Now the cutters are in halves,
and while one set F is cutting, and advancing axially, the other
set G, being out of the cut, is returning. The method appears
complicated, but in reality is very simple, and the wheels thus
cut will gear together most correctly, without backlash. By a
more recent method, a single emery wheel, of correct section,
rotates in one place while the wheel is really rolled along a line
parallel to the grinding axis; and thus cast wheels may be
trued up.

If a milling machine be not at hand, very good wheel-cutting
can be done in the lathe. The lathe centres support; a mandrel
which carries the blank, and the milling cutter is fixed on a